Conventional actuating devices for an electrical power wrenches known to applicant are respectively disclosed in U.S. Pat. No. 4,920,831 assigned to Dora Hsiao Ling Huang with the title of "VEHICLE-CARRYING PURPOSE WRENCH", U.S. Pat. No. 5,740,892 to Chen Shu-Hsia Huang with the title of "POWER WRENCH TORQUE TRANSMISSION MECHANISM" and U.S. Pat. No. 5,035,161 to Dora H. Huang with the title of "WRENCH". All of the cited U.S. Patents concern a transmission device to produce an intermittent torque so as to loosen/tighten a bolt or a nut. Nevertheless, the wrenches cited in the mentioned patents involve a complicated structure and too many parts that takes time to assemble and maintain.
The present invention intends to provide an actuating device for an electrical power wrench wherein the output shaft has a plate mounted thereto which is radially impacted by a pin controlled by the eccentric force of the power wrench. The pin extends and radially impacts the plate when the desired eccentric force of the base member driven by a motor is reached. The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional power wrenches.